Sex differences in brain mechanisms of pain and placebo analgesia

Information that a painkiller has been administrated decreases reported pain, and decreases activity in pain related areas of the brain. Expectations of pain relief activate pain inhibitory opioid mechanisms, which reduce the pain signal. Placebo analgesic responses have been found to be stronger in males, suggesting that the pain inhibitory system involved in placebo analgesia is more efficient in males. Findings in support of this are that some analgesics are more efficient in males, and that procedures that activate the pain inhibitory system have greater effect in males. Also, this pain inhibitory mechanism seems to be dysfunctional in patients with chronic pain, where females are overrepresented.

The project investigates a) whether a common mechanism can explain placebo analgesia, the effect of opioids, and gender differences in response to opioids, b) the role of stress and emotion in placebo effects, c) whether individual differences in pain and stress levels can be related to placebo responding.

Placebo effects on pain are assessed by verbal pain report with VAS or NRS. Emotions, arousal and stress are assessed with standardized questionnaires. Brain mechanisms underlying the placebo effect are investigated by the use of fMRI and EEG. Peripheral physiological responses to placebos are studied with heart rate variability (HRV) which indexes sympathetic and parasympathetic activation.

The project is multidisciplinary: researchers in the fields of biological and cognitive psychology, electrophysiology, anaesthesiology and pharmacology collaborate in the project. Successful completion of the project will bring new insights in the understanding of pain and pain treatment.